Chromatography

Question 1

What is the principle of chromatography?

Answer 1

Some solutes are more soluble than others in the same solution. This allows different pigments to be identified.

Question 2

How do you prepare a chromatogram?

Answer 2

1) Draw a pencil line a few cm from the bottom of the tank and suspend it in the tank with the pencil line above the level of the suitable solvent.
2) Use a micropipette to make a concentrated spot on the pencil line. Place a drop, allow it to dry and so on.
3) Make sure the spot is as small as possible.

Question 3

Running the chromatogram.

Answer 3

Make sure that :

1) The pencil line is above the line of the solvent
2) The chromatogram is securely attached
3) The chromatogram is not suspended at an angle.
4) You stop the chromatogram before it reaches the end of the paper.

Question 4

Developing the chromatogram

Answer 4

1) Dry it

2) Mark the solvent front with a pencil.

Question 5

What precautions must you take to ensure validity?

Answer 5

Only hold the chromatogram at the edges to prevent contamination
Don’t lay it on your bench
Leave the solvent in the tank for a suitable length of time allowing for it to become saturated.

Question 6

How do you calculate Rf?

Answer 6

Distance moved by solute
Rf = —————————————– always < 1
Distance moved by solvent

Question 7

Why do leaves become yellow / yellow-brown in Autumn?

Answer 7

The green chlorophyll is broken down and valuable nutrients withdrawn into the tree, leaving less valuable pigments and waste products.